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Fix Query Issues

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Query Targeting alerts indicate inefficient query or queries.

Alert Conditions

You can configure the following alert conditions in the project-level alert settings page to trigger alerts.

Query Executor: Scanned / Returned occurs if the number of index keys examined to fulfill a query relative to the actual number of returned documents meets or is above a certain threshold.

Query Executor: Scanned Objects / Returned occurs if the number of documents examined to fulfill a query relative to the actual number of returned documents meets or is above a certain threshold.

Common Triggers

  • No index that supports a given query or queries.
  • Existing index can only partially support a query or queries.

Fix the Immediate Problem

The Performance Advisor provides the easiest and quickest way to create an index. The Performance Advisor monitors queries that MongoDB considers slow and recommends indexes to improve performance.

Click Create Index on a slow query for instructions on how to create the recommended index.

Note

It is possible to receive a Query Executor alert for an inefficient query without receiving index suggestions from the Performance Advisor if the query exceeds the slow query threshold and the ratio of scanned to returned documents is greater than the threshold specified in the alert.

In addition, you can use the following resources to determine which query generated the alert:

  • The Real-Time Performance Panel monitors and displays current network traffic and database operations on machines hosting MongoDB in your MongoDB Atlas clusters.

  • The MongoDB logs maintain an account of activity, including queries, for each mongod instance in your MongoDB Atlas clusters.

  • The cursor.explain() command for mongosh provides performance details for all queries.

  • The Data Profiler records operations that MongoDB Atlas considers slow when compared to average execution time for all operations on your cluster.

    Note

    Enabling the Database Profiler incurs a performance overhead.

Implement a Long-Term Solution

To learn more about query performance, see:

Monitor Your Progress

Ops Manager provides two methods to visualize query targeting:

  • Query Targeting metrics, which highlight high ratios of objects scanned to objects returned.
  • The Profiler, which describes specific inefficient queries executed on the cluster.

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